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Wsm2110 / Faster.Map

Faster.Map is a high-performance, thread-safe key-value store designed to outperform the standard Dictionary and ConcurrentDictionary
MIT License
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Question about Fmix pipelining friendliness #25

Closed miroslavp closed 1 year ago

miroslavp commented 1 year ago

Are you sure this code is pipelining friendly? It looks quite the opposite to me. Every line relies on the result from the previous line. https://github.com/Wsm2110/Faster.Map/blob/10ed34a1f5c3428cdb1dd5910e0597645343d895/src/DenseMapSIMD.cs#L812-L815

The generated asm code also doesn't suggest pipelining friendliness.

       8BC1                 mov      eax, ecx
       C1E810               shr      eax, 16
       33C1                 xor      eax, ecx
       69C86BCAEB85         imul     ecx, eax, 0xFFFFFFFF85EBCA6B
       8BC1                 mov      eax, ecx  ;in order to start the calculations on the second line we need the result from ecx (previous line)
       C1E80D               shr      eax, 13
       33C1                 xor      eax, ecx
       69C835AEB2C2         imul     ecx, eax, 0xFFFFFFFFC2B2AE35
       8BC1                 mov      eax, ecx  ;here again we need the result from the previous line in order to calculate the return value
       C1E810               shr      eax, 16
       33C1                 xor      eax, ecx

Am I missing something?

Wsm2110 commented 1 year ago

Just a way to mix the order of bits and retrieve an index, nothing fancy.